Controllable pitch propeller and drive means therefor

ABSTRACT

A controllable pitch propeller is provided in which the blades are rotatably mounted on a hollow hub having an axial bore, the wall of which is of non-circular cross-section, and control of the pitch of the blades is effected by a pair of axially-threaded nuts slidably mounted in said axial bore, and a single doublethreaded control screw threadedly connected with said nuts. The blades are mounted on the hub in a novel manner which strengthens the attachment of the blades to the hub, and permits removal or replacement of the blades without disturbing other parts involved in the assembly of the blades with the hub. A differential assembly is provided for driving the propeller and the control screw at the same speed, as well as power driven means for driving the control screw at a speed different from that of the output shaft, whereby the aforesaid nuts are moved relatively to each other without interfering with the rotation of the hub. Means are also provided for indicating the pitch position of the blades and for activating the power driven means for driving the control screw.

CONTROLLABLE PITCH PROPELLER AND DRIVE MEANS THEREFOR Inventor: WilliamB. Herbert, 111 Yantacau Brook Rd, Montclair, NJ. 07043 Filed: July 21,1971 Appl. No.: 164,502

[52] US. Cl 416/207, 416/160, 416/162, 416/163, 416/165, 416/167 [51]Int. Cl B63h 3/02 [58] Field of Search... 416/151, 155, 160, 162, 163,416/165, 136, 152, 167, 204, 205, 207, 166, 159

[56] References Cited UNITED STATES PATENTS 2,360,982 10/1944 Sahle416/160 X 2,389,663 11/1945 Forsyth 416/162 2,548,045 4/1951 Nichols416/155 2,629,451 2/1953 Nichols 416/155 2,675,084 4/1954 Nichols416/160 v 2,711,796 6/1955 Amiot 416/163 UX FOREIGN PATENTS ORAPPLICATIONS 590,312 l/1960 Canada 416/163 855,435 ll/l960 GreatBritain.... 416/155 860,205 2/1961 Great Britain 416/163 Mar. 5, 1974 [57 ABSTRACT A controllable pitch propeller is provided in which theblades are rotatably mounted on a hollow hub having an axial bore, thewall of which is of non-circular cross-section, and control of the pitchof the blades is effected by a pair of axially-threaded nuts slidablymounted in said axial bore, and a single double threaded control screwthreadedly connected with said nuts. The blades are mounted on the hubin a novel manner which strengthens the attachment-of the blades to thehub, and permits removal or replacement of the blades without disturbingother parts involved in the assembly of the blades with the hub. Adifferential assembly is provided for driving the propeller and thecontrol screw at the same speed, as well as power driven means fordriving the control screw at a speed different from that of the outputshaft, whereby the aforesaid nuts are moved relatively to each otherwithout interfering with the rotation of the hub. Means are alsoprovided for indicating the pitch position of the blades and foractivating the power driven means for driving the control screw.

6 Claims, 9 Drawing Figures PATENTEUHAR 51914 3.795.463

Sam 1 0F 5 BY 9 WBLLBAM B. HERBERT INVENTOR.

ATTORNEYS PATENTED 74 SHEET 2 OF 5 mm m. mm

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INVENTOR. WILLEAM B. HERBERT ATTORNEYS PAIENTEDKAR 5W 3395.433

SHEET 8F 5 69 gg INVENTOR. 5 WELLBAM B. HERBERT TZZVLE'W ATTORN EYSPATENTEDHAR SIBM SHEE? g 8? INVENTOR.

WELUAM B. HERBERT ATTQNEYS CONTROLLABLE PETER lPROlPlElLLER AND DRHVEMEANS THEREFGR This invention relates generally to controllable pitchpropellers and to driving means therefor, but has reference moreparticularly to pitch controlling means and driving means for propellersused in connection with marine drive or propulsion systems.

in the Gloor US. Pat. No. 1,396,325, a screw propeller is disclosed inwhich the blades are reversible relatively to the longitudinal axis ofthe propeller shaft, and a reversing or feathering mechanism isprovided.

The propeller blades are formed at their inner ends with cylindricalstems which are mounted for rotation about their longitudinal axes in ahollow boss or hub. The stems are integral with the propeller blades,and are formed with a plurality of annular ribs, so that in assemblingthe blades with the hub, it is necessary to make the intermediateexternally cylindrical section of the hub in two parts and to providebolts for connecting said parts to each other.

From each stern a pair of parallel pins project eccentrically intoadjacent slides movable in grooves or recesses of separately movablewings. These wings are so disposed relatively to each other as toslidably engage or interengage with one another.

The wings are mounted on the ends of members which project into thehollow boss or hub, and by moving such members longitudinally inopposite directions, the slides within the grooves or recesses of thecorresponding wings will move transversely of the wings, and thepropeller blades will be turned about their longitudinal axes, therebyreversing or feathering the blades.

One of the aforesaid members is a tubular member mounted forlongitudinal movement in a hollow portion of the main propeller shaft,and the other member is a solid rod mounted for longitudinal movementinside the first or tubular member, both members being thus concentricwith and adapted to revolve with the propeller shaft.

Due to the fact that one of said members slides inside the other, thereis constant friction therebetween, as well as between parts of themechanism which causes relative longitudinal movement of said members,including collars, spokes and disks. in other words, the forcesnecessary to either rotate the propeller blades or prevent them fromrotating, must necessarily be carried up to the control handle or leverto obtain or to hold the position of the blade, and this has been foundto be highly disadvantageous in a controllable pitch propeller.

The present invention has as its primary object, the provision of acontrollable pitch propeller which overcomes all of the disadvantages ofthe mechanism disclosed in the aforesaid Gloor patent.

Another object of the invention is to provide a. controllable pitchpropeller in which the propeller blades are attached to the intermediateexternally cylindrical section of the hub in such a manner that theintermediate section of the hub can be made in one part, instead of twoparts, thereby reducing costs, and dispensing with the need for bolts orother fasteners for connecting the two parts.

Another object of the invention is to provide a controllable pitchpropeller of the character described, in which the intermediateexternally cylindrical section of the hub is provided with an internalcavity for the reception of pitch operating nuts, the wall of whichcavity is of non-circular, i.e., of triangular or polygonalcrosssection, in contrast to a cavity of circular cross-section, wherebythe size of the propeller blade stems, pitch operating nuts and otherinternal parts may be increased for a given size of hub, withcorresponding increase in strength of such parts.

Another object of the invention is to provide a controllable pitchpropeller of the character described, which is characterized by the useof a single screw shaft or rod for actuating pitch operating nuts,whereby all of the forces involved in rotating the blades to control thepitch of the latter, are completely confined to the internal threads inthe pitch operating nuts, and within a relatively short length orsection of said screw shaft or rod.

A further object of the invention is to provide a controllable pitchpropeller and operating mechanism therefor, in which frictionalresistance between parts is reduced to a minimum, and assembly of theparts is greatly facilitated or simplified.

A still further object of the invention is to provide a novel doubledifferential device for the controllable pitch propeller, which enablesthe pitch of the propel ler blades to be controlled while the propellerand driving means therefor are rotating.

Other objects and advantages of my invention will be apparent during thecourse of the following description.

in the accompanying drawings forming a part of this specification, andin which like numerals are employed to designate like parts throughoutthe same,

FIG. 1 is a fragmentary schematic or diagrammatic view showing thecontrollable pitch propeller system, embodying the invention;

HO. 2 is a view, partly in elevation and partly in section, showing acontrollable pitch propeller and a portion of the operating mechanismtherefor;

FlG. 3 is a view, partly in elevation and partly in section, showing theother portion of the operating mechanism, including the doubledifferential device;

FlG. 4 is a view, partly in cross-section and partly in elevation,showing the pitch operating nuts in an advanced position relatively toeach other;

HG. 5 is a view similar to H6. 4, but showing the pitch operating nutsin a retracted position relatively to each other.

HO. 6 is a fragmentary crosssectional view, taken on the line 6--6 ofH6. 4, but showing portions of the propeller blades and the manner ofattachment of the blades to the blade roots;

HO. 7 is a view showing the pitch operating nuts and control screwtherefor, independently of the propeller;

HO. 8 is a cross-sectional view, taken on the line 8-8 of FIG. 7, and

FIG. 9 is a cross-sectional view,'taken on the line 9-9 of PK]. 7..

Referring more particularly to the drawings, and especially to H6. 1,there is illustrated, in somewhat diagrammatic or schematic fashion, theaft portion it) of a boat, a propeller llll, a propeller drive shaft 12,a V- drive 13 for the propeller shaft, an engine 14 for the V- drive, adouble differential device 15 for controlling the pitch of the blades ofthe propeller it, and means 15a for indicating the position of thepropeller blades and for activating the control mechanism.

The propeller 11 comprises a tubular hub 16 having a cylindrical outersurface 17 and an axial cavity or bore defined by flat surfaces or sidesl8, l9 and 20, a diametric cross-section through this cavity or borebeing in the form of an equilateral triangle. It is to be understood, inthis connection, that the number of surfaces defining this axial cavityor bore will correspond to the number of propeller blades of thepropeller, which, in this instance, is a three-bladed propeller. Thus,in a four-bladed propeller, the number of surfaces or sides would befour; in a five-bladed propeller, the number of surfaces or sides wouldbe five. In a twobladed propeller, the cavity would be square orrectangular in cross-section.

' Extending radially through the wall of the hub 16, from the surfaces18, i9 and 20, to the surface 17, are circumferentially-spaced bores 21,22 and 23 (see FIG. 6), these bores having annular grooves or recesses24 of V-shaped cross-section in the walls thereof adjacent theirradially-outer ends, for a purpose to be presently described.

The number of such radial bores, shown in this instance as three,corresponds with the number of propeller blades, so that it is to beunderstood that the number of bores is not limited in respect to thisinvention.

Secured to the rear end of the hub 16, as by means of socket head screws25, is a conical cap 26.

The hub 16, in turn, is secured as by means of socket head screws 27, tothe driven section 28 of the hollow or tubular propeller shaft 12.

The driven section 28 of the propeller shaft is connected, as by screws29, to a collar 30, which is connected, as by screws 31., to a secondcollar 32. The collar 32 is connected, as by screws 33, to a tubularoutput shaft 34, which is a part of the V-drive 13. The output shaft 34is mounted for rotation in bearings 35 and 36 mounted in axially-alignedopenings 37 and and 38 respectively of the housing 39 of the V-drive 13.The bearings 35 and 36 are retained against displacement by cover plates40 and 4H secured to the housing 39.

The \/-drive 13 includes a bevel pinion 42, which drives a bevel gear43, which, in turn, drives the output shaft 34 of the V-drive.

The propeller, in this case, comprises three circumferentially-spacedblades 44, 45 and 46 of identical construction.

Each blade is secured, as by means of four circumferentially-spaced capscrews 47, to a conical blade base 48 disposed in the outer end of thebore 21, 22 or 23. The blade base is provided withcircumferentiallyspaced unthreaded openings 50 for passage therethroughof the screws 47. The screws 47 are threadedly secured to an annularblade root 51 disposed in the inner end of the bore 21, 22 or 23, andhaving a conical portion 52. The blade root 51-52 is provided withthreaded openings 53 for receiving the ends of the screws 47.

For the purpose of securing the blade base 48 to the blade root 51-52,prior to attachment of the blade to the blade base and blade root, asocket head screw 54 is provided, which extends through an unthreadedcentral opening 55 in the blade base 48, and is threaded into a threadedopening 56 of the blade root. The blade 44 is provided with a centralhole 57 into which the head of the screw 54 extends when the blade issecured to the blade base and blade root.

For the purpose of aligning the openings 50 with the openings 53, whenassembling the blade base and blade root, a dowel pin 58 is provided,which extends into the blade base and blade root, and locates theseparts in proper circumferential relationship to each other for assembly.

The blade base 48 and conical portion 52 of the blade root 51respectively coact with the annular grooves or recesses 24 to confinetherebetween a bearing 59, which may be bearing rollers, bearing ballsor non-rolling segments of a ring, which results in a plain bearingmounting instead of an anti-friction bearing.

The aforesaid method of connecting the blades to the blade roots,strengthens the attachment of the blades to the blade bases and to theblade roots and provides proper load to bearing surfaces for the bearingrollers. This method of anchoring the blades also permits removal and/orreplacement of a blade without disturbing the other parts involved inthe assembly.

Each blade root 51 has mounted in its inner end a pair of rotatable pins60 and 61 spaced from each other diametrically of the inner face of theblade root, and respectively provided with a rectangular slide block 60aand 61a formed integrally with the pin.

Mounted for slidable axial movement in the axial cavity or bore of thehub 16 is a pair of nuts 62 and 63 for controlling the pitch of thepropeller blades.

The nut 62 has a triangular portion 64 conforming in contour to theaxial cavity or bore of hub 16, and having a threaded axial bore 65extending therethrough, while the nut 63 has a similar triangularportion 66 conforming-in contour to the axial cavity or bore of the hub16, and having a threaded axial bore 67 extending therethrough, which isof slightly larger diameter than the bore 65 and the threads of whichare of opposite hand to the threads of the bore 65.

The portion 64 of the nut 62 is provided with fingers or extensions 68,69 and 70, spaced circumferentially about the axis of the bore 65, andextending from the inner face of the portion 64 (see FIGS. 7 and 8), andare of the contour shown in FIG. 8. The fingers or extensions 68, 69 and76 are provided respectively in one face thereof with slots or grooves68a, 69a and 70a, these slots or grooves lying in a common planetransversely of the nut 62.

The portion 66 of the nut 63 is similarly provided with fingers orextensions 71, 72 and 73, spaced circumferentially about the axis of thebore 67, and extending from the inner face of the portion 64 (see FIGS.7 and 9), and are of the contour shown in FIG. 9.

The fingers or extensions 71, 72 and 73 are arranged or spacedcircumferentially to alternate with the fingers or extensions 68," 69and 70, so that when the nuts are in the position shown in FIGS. 4, 5and 6, the fingers 71, 72 and 73 extend into and fill the spaces betweenthe fingers 68, 69 and 70 and slide along the latter fingers. Thefingers 71, 72 and 73 are provided respectively in one face thereof withslots or grooves 71a, 72a and 73a, these slots or grooves lying in acommon plane transversely of the nut 63.

As seen in FIGS. 4, 5 and 6, the block 66a of the blade root 51 of theblade 44 lies in the slot or groove 69a of the finger 69, while theblock 61a of that blade root lies in the slot or groove 71a of thefinger 71. As seen in FIG. 6, the block 60a of the blade root 51 of theblade 45 lies in the slot or groove 68a of the finger 68,

while the block 61a of that blade root lies in the slot or groove 72a ofthe finger '72, and the block btlla of the blade root 51 of the blade 46lies in the slot or groove 70:! of the finger 74 while the block 61a ofthat blade root lies in the slot or groove 73a of the finger 73.

For the purpose of moving the nuts 62 and 63 toward and away from eachother, a control screw 74 is provided having threads 7S, which are inthreaded engagement with the threads of the bore 67 in the nut 63, andthreads 76 which are in threaded engagement with the threads of the bore65 in the nut 62. Since the threads of the bore 67 are of opposite handto those of the threads in the bore 65, it follows that rotation of thecontrol screw 74 in one direction will cause the nuts 62 and 63 to moveaway from each other, and that rotation of the control screw 74 in theopposite direction will cause the nuts 62 and 63 to move toward eachother. Such movement of the nuts away from each other, that is to say,from the position shown in FllG. 4 to that shown in FIG. 5, will causethe blocks 60a and 61a to move from the position shown in FlG. 4 to thatshown in FIG. 5, and the other sets of blocks to move correspondingly,thereby causing the propeller blades to be rotated about theirlongitudinal axes in an obvious manner, for controlling the pitch of theblades.

The control screw '74 is keyed to a coupling member 77, which isinterlocked with a coupling member 78. This coupling may, for example,be a Boston coupling No, FCBBlS.

The coupling member '78 is secured to the after end of a control shaft79, which is mounted for rotation in radial thrust bearings 8t) and 8Hmounted in the driven section 28 of the propeller shaft. The bearing 84is retained against axial displacement relatively to the driven section28 by means of a snap ring 83 secured to the shaft 79 adjacent thebearing fill.

Rearwardly of the bearing 81, the shaft 79 is of reduced diameter, thisportion being designated by reference numeral 791:, and referred tohereinafter as the control shaft.

The control shaft 79a extends axially through the output shaft 34- andinto a differential assembly to be presently described, a portion 79b ofthis control shaft intermediate its ends being threaded for a purpose tobe also presently described.

For the purpose of controlling the circumferential position of thecontrol shaft 79a relatively to that of the output shaft 34, and therebycontrolling the pitch of the propeller blades, a differential device isprovided, which is rigidly supported by bracket arms or bars 83 and 8dextending from the housing of the V-drive 113, and which is housedwithin a housing 85 provided with end plates 86 and 87, this housinghaving a motor 88 mounted thereon.

This differential device comprises a planetary carrier 89, mounted forrotation in the end plate 87, and adapted to be driven at such timesthat the pitch of the propeller blades is to be changed, by the motor 88through the intermediary of idler mechanism 9i) and a suitable belt,gear or worm reduction, indicated generally by reference numeral 911.

The carrier 89 carries cantilever supports 92 for bearing shafts 93 and94.

The differential device further includes a flanged member 95 mounted forrotation in the end plate se and normally driven by guide rods 96 and 97extending from the output shaft 34. The member 95 is pinned to a bevelgear 98, which drives a bevel gear 99 mounted for rotation about astationary bearing shaft 100 affixed to the housing 85. The gear 99, inturn, drives bevel gears Hill and MP2 which idle on the control shaft79a. The gears Mill and MP2 are rigidly interconnected as a unit by apin M1 3, and the gear W2 drives'bevel gears 1104 and W5, which arerotatably mounted on bearing shafts 93 and 9drespectively.

The bevel gears MM and M95 are in driving engagement with a bevel gearres, which is keyed to the control'shaft 79a, and which is rotatablerelatively to the planetary carrier 89,

Means have also been provided, generally designated hereinbefore byreference numeral 15a, for achieving the dual function of activating themotor 88 and indicating visually the position or pitch setting of thepropeller blades.

Such means includes the guide rods 96 and 97, to which reference haspreviously been made, and comprises an axially movable disk W7 for whichthe rods 96 and 97 serve as guides, a sliding bearing 108 supported on astationary support MP9, an operating block 1110, switches 111111 and M2carried by the blocks 110 and provided with actuating buttons, operatingarms It 13 and 114i carried by the bearing MP8, and rollers 115 and 116revolubly supported by the upper ends of the arms 1113 and 11114respectively, and adapted to engage the opposite faces of the disk W7,

The block lllll is positioned along the bearing 108 by means of anysuitable remote control device such, for example, as a flexiblepush-pull cable (not shown).

When the pitch of the propeller blades is not to be changed, the motor88 is not energized, and consequently, the output shaft 34 drives theguide rods 96 and 97, member 95, bevel gears 98, 99, i0 102, 104 and105, and the control shaft 79a, the planetary carrier 89 remainingmotionless. The output shaft 34 and control shaft. 79:: therefore rotateat the same or identical speed, and, consequently, no pitch change willtake place in the propeller. The effect, in other words, is tantamountto having the output shaft, control shaft and nuts 62 and d3 lockedtogether as a unit. At the same time, the disk W7, although rotated bythe guide rods 96 and 97, will not be moved axially, even though it isin threaded engagement with the control shaft 79a.

With the propeller either rotating or at rest, the lever arms R113 andill- 3 are held together by a spring 117, with the rollers M5 and lid incontact with the disk 107.. When the pitch of the propeller blades is tobe changed, movement of the operating block 110 to the left, as viewedin FIG. 3, will cause the disk MP7 to interfere with free movement ofthe roller 1116, thereby displacing lever and removing pressure from theswitch ll 12, closing the control circuit to motor 28, thus rotating theplanetary carrier.

Rotation of the planetary carrier 89 causes rotation of the controlshaft 79a at a speed different from that of the output shaft 34, therebychanging the pitch setting of the propeller blades. As the pitchchanges, disk 107 will move along the shaft 79a to the left, allowingspring 1117 to return lever illl ll to its normal position. in thisposition, lever M4 depresses the actuating button of switch 1112,opening the circuit to motor 88, and resulting in the cessation of thepitch changing movement. Movement of the block ill) to the right willresult in a similar cycle, but in the opposite direction.

In either case, the disk H07 moves a distance corresponding to thedistance through which the block 110 has been moved, and the position ofthe disk, at such time, will indicate visually the position or pitchsetting of the propeller blades.

The function of the differential assembly, which has been described, isto enable this control operation to take place while the propeller andthe complete drive train therefor are rotating.

It is to be noted, in particular, that the entire pitch control orfeathering action is confined within the relatively short length of thehub 16, through the medium of a single double-threaded, control screw74, which is also located within the hub. The forces involved inrorating the propeller blades forpitch control or for resisting rotationof the propeller blades by external forces are, accordingly, completelyconfined to the internal threads in the pitch operating nuts, and to arelatively short section or length of the control screw.

This arrangement represents a marked improvement over that disclosed inthe Gloor patent, in that it eliminates all of the disadvantages of theGloor patent to which reference has been made, and provides an operatingmechanism in which frictional resistance between parts is reduced to aminimum, and assembly of the parts is greatly simplified.

The threaded axial bores as and 67 of the nuts 62 and 63, as well as theportions 75 and '76 of the control screw '74 need not be of differentdiameters, and may be of the same diameter. Moreover, the use ofacontrol screw 74 which is independent of the coupling 77-78 enables thenuts 62 and 63 to be assembled from either end with the control screwbefore the coupling is installed.

Another advantage of the present invention resides in the fact that thepropeller blades are attached to the intermediate externally-cylindricalsection of the hub in such a manner that this section of the hub can bemade in one part, instead of two parts, as in Gloor, thereby reducingcosts, and dispensing with the need for bolts or other fasteners forconnecting the two parts.

Another advantage resides in the fact that blade bases and blade rootsare utilized in assembling the propeller blades with the hub, so thatthe method of connecting the blades to the blade roots strengthens theattachment of the blades to the blade bases and to the blade roots andprovides proper load to bearing surfaces for the bearing rollers orother bearing means utilized. It also permits removal and/or replacementof a blade without disturbing the other parts involved in the assembly.

The use of a propeller hub having an internal cavity for the receptionof the pitch controlling nuts, the wall of which is of triangular orpolygonal cross-section permits the size ofthe propeller blade stems,pitch controlling nuts, and other internal parts to be increased for agiven size of hub, with corresponding increase in the strength of suchparts.

The use of the double differential assembly enables the propeller pitchsettings to be controlled through power driven means, and while thepropeller and the complete drive train therefor are rotating.

The use of the indicator disk and switches provides a convenient methodof indicating visually the position or pitch setting of the propellerblades, as well as activating the motor.

It is to be understood that the form of my invention, herewith shown anddescribed, is to be taken as a preferred example of the same, and thatvarious changes may be made in the shape, size and arrangement of partsthereof, without departing from the spirit of the invention or the scopeof the subjoined claims.

I claim:

1. in a controllable pitch propeller, a hub having an axial bore, pitchadjusting means within said bore, a plurality ofcircumferentially-spaced bores extending from said axial bore throughsaid hub, and having their axes radial to said hub, said last-namedbores having the same diameter at their radially innermost and radiallyoutermost ends, blade roo'ts mounted in said radial bores adjacent theradially-innermost ends of said radial bores and having a maximumdiameter not greater than the diameter of said radially-innermost ends,blade bases independent of said blade roots and mounted in said radialbores, said blade bases having a maximum diameter not greater than thediameter of said radially-outermost ends, means for removably securingsaid blade bases to said roots, blades independent of said blade rootsand blade bases and having inner end portions of the same diameter assaid radially-outermost ends, means independent of said firstnamedsecuring means for removably securing said blades to said blade rootsand blade bases, said radial bores in said hub having annular recessesin the walls thereof intermediate the ends of each of said bores, andsaid blade bases and blade roots having surfaces coacting with eachother and with the walls of said recesses to define annular hollowspaces for the reception of bearings.

2. A controllable pitch propeller, as defined in claim I, wherein saidfirst-named securing means comprises a headed screw having a sternextending centrally through the blade base and in threaded engagementwith said blade root.

3.. A controllable pitch propeller, as defined in claim 2, wherein saidlast-named securing means comprises a plurality of headed screws spacedcircumferentially about the longitudinal axis of the blade and extendingthrough the blade base, and in threaded engagement with the blade root.

4. A controllable pitch propeller, as defined in claim 3, wherein theblade covers the head of said firstnamed securing means.

59 A controllable pitch propeller, as defined in claim 1, wherein rollerbearings are disposed in said annular spaces.

6. A controllable pitch propeller, as defined in claim 1, wherein ballbearings are disposed in said annular spaces.

1. In a controllable pitch propeller, a hub having an axial bore, pitchadjusting means within said bore, a plurality ofcircumferentially-spaced bores extending from said axial bore throughsaid hub, and having their axes radial to said hub, said last-namedbores having the same diameter at their radially innermost and radiallyoutermost ends, blade roots mounted in said radial bores adjacent theradially-innermost ends of said radial bores and having a maximumdiameter not greater than the diameter of said radially-innermost ends,blade bases independent of said blade roots and mounted in said radialbores, said blade bases having a maximum diameter not greater than thediameter of said radially-outermost ends, means for removably securingsaid blade bases to said roots, blades independent of said blade rootsand blade bases and having inner end portions of the same diameter assaid radially-outermost ends, means independent of said first-namedsecuring means for removably securing said blades to said blade rootsand blade bases, said radial bores in said hub having annular recessesin the walls thereof intermediate the ends of each of said bores, andsaid blade bases and blade roots having surfaces coacting with eachother and with the walls of said recesses to define annular hollowspaces for the reception of bearings.
 2. A controllable pitch propeller,as defined in claim 1, wherein said first-named securing means comprisesa headed screw having a stem extending centrally through the blade baseand in threaded engagement with said blade root.
 3. A controllable pitchpropeller, as defined in claim 2, wherein said last-named securing meanscomprises a plurality of headed screws spaced circumferentially aboutthe longitudinal axis of the blade and extending through the blade base,and in threaded engagement with the blade root.
 4. A controllable pitchpropeller, as defined in claim 3, wherein the blade covers the head ofsaid first-named securing means.
 5. A controllable pitch propeller, asdefined In claim 1, wherein roller bearings are disposed in said annularspaces.
 6. A controllable pitch propeller, as defined in claim 1,wherein ball bearings are disposed in said annular spaces.